You stand still and jump in the air and pull your knees to your stomach. Make sure your feet are not going to your booty but that are parallel with the floor.
Practice it.
arms up and jump and while you jump, tuck at the same time
Tuck Jump, Pike Jump, Straddle Jump, Swivle Hips, Barani, Somersault... There are just a few of many.
pike, straddle, split, tuck, layout, hollow, arch, and open or closed hip position
Tuck Jump, Pike Jump, Straddle Jump, Swivle Hips, Barani, Somersault... There are just a few of many.
Jump and tuck your head and exhale through your nose and just keeping practicing!! 
A tu is when a gymnast folds her knees into her chest. This can be done in a jump or a flip.
Tuck jumps primarily engage the quadriceps, hamstrings, and glutes as they power the explosive jump. Additionally, the calves contribute to the push-off, while the core muscles, including the abdominals and obliques, stabilize the body during the jump and landing. This compound movement also involves the hip flexors as you pull your knees toward your chest. Overall, tuck jumps provide a full-body workout, enhancing strength and coordination.
Jumping jack, tuck jump, squat thrust, push ups, sit ups, sprint.
handstand, forward roll, tuck jump dismount, side handstand dismount
There are many different skills! They range from a tuck jump to a back tuck. In all levels you compete floor,vault,beam, and bars but they are all different skills according to level.
You dont, what you do is ride it and tuck up your bike under you. Because you want to go fast, but you dont wanna go high.